A rolling cone earth boring bit has a body with a threaded end that attaches to a drill string. The body normally has three depending bearing pins, each supporting a cone rotatably mounted thereon. Each cone has cutting elements on its exterior for disintegrating the earth formation as the bit body is rotated. Each cone has a cavity that slides over one of the bearing pins. A lubricant reservoir supplies lubricant to the spaces between the cone cavity and bearing pin. Normally, the lubricant system also has a pressure compensator for equalizing the lubricant pressure with the pressure of the borehole drilling fluid on the exterior of the bit. A sealing arrangement located near the mouth of each cone seals the lubricant from the borehole fluids.
If the sealing arrangement begins to leak, the bit would soon fail and have to be retrieved. This could occur before the cutting structure on the cone has worn out, thus shortening the life of the bit. Because of the importance of having a durable sealing arrangement, many varieties have been used and proposed over the years. In one type, a seal groove is formed in the cone cavity near the mouth of the cone. The groove has a base and two parallel side walls. An elastomeric seal ring fits within the groove and seals between the base and the bearing pin.
The seal ring may be a type referred to as a high aspect ratio seal ring. A high aspect ratio seal ring has a radial dimension measured from its inner diameter to its outer diameter that is greater than its thickness, measured from one side surface to the other. The seal groove has a depth that is greater than its width. Sealing engagement occurs between the outer diameter of the seal ring and the groove base and between the inner diameter of the seal ring and the bearing pin. The side surfaces of the seal ring do not sealingly engage the side walls of the groove. Normally, the width of the groove is appreciably larger than the width of the seal ring so as to allow the seal ring to thermally expand during use.
A disadvantage of having clearances between the seal ring side surfaces and the groove side walls is that the seal ring may initially become misaligned or skewed relative to the groove. If so, the misalignment may cause a different contact pressure than desired between the seal ring and the seal groove and the bearing pin. The different contact pressure could result in seal failure.